Such a method if known from the German offenlegungsschrift 27 59 126 in which a light source is described that irradiates the milk and in which a light-sensitive element is described by means of which a color change of the milk is determined. When the milk shows a deviating color, such as due to the presence of blood or pus, the milk is separated and collected in a separate reservoir. This method has the disadvantage that only rough deviations in the color of the milk can be determined and that subtle color differences, such as due to the presence of exiguous contaminations or as a result of the fact that the animal has consumed grass, instead of concentrate, are not detected.
An alternative method is known from the document Dutch Application NL 1004980. This document discloses a method in which the intensity values of a number of colors in the milk are determined and in which the milk is produced by individual animals. By comparing the intensity values with the values recorded during previous milkings, the presence of specific substances, such as contaminates can be determined. This method has the disadvantage that the intensity values of the milk vary to a great extent, depending on the amount of surrounding light. Moreover, the results cannot be interpreted quantitatively, as only changes relative to previous milkings are recorded.
Finally document Dutch Application NL 94022010 describes a sensor for the detection of contaminates in the milking systems of a milking machine, making use of radioactive radiation or ultrasonic sound. This sensor has the disadvantage of only being suitable for detecting contaminates in the milk and not being able to perform other qualitative measurements on the milk, such as detecting blood, diagnosing mastitis or determining the cell count.